BUG: Frequency shift on empty DataFrame doesn't shift index

[colinc719]

Pandas version checks

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Reproducible Example

dates = pd.date_range('2020-01-01', '2020-01-03')
df = pd.DataFrame(index=dates, columns=[])
day = pd.offsets.Day()
shifted_dates = df.shift(freq=day).index
assert (shifted_dates == dates + day).all()

Issue Description

Running DataFrame.shift with freq on a DataFrame with empty columns does not shift the index.

Expected Behavior

I would expect DataFrame.shift to shift the index similarly to how it would if the DataFrame had columns. Particularly with the above example, I would expect df.reindex(['A'], axis=1).shift(freq=day).reindex([], axis=1) to be equivalent to df.shift(freq=day).

Installed Versions

INSTALLED VERSIONS

commit : 91111fd
python : 3.10.13.final.0
python-bits : 64
OS : Linux
OS-release : 5.15.102.hrtdev
Version : #1 SMP Tue Mar 14 13:23:09 EDT 2023
machine : x86_64
processor :
byteorder : little
LC_ALL :
LANG : en_US.UTF-8
LOCALE : en_US.UTF-8

pandas : 1.5.1
numpy : 1.23.2
pytz : 2022.1
dateutil : 2.8.2
setuptools : 62.1.0
pip : 24.2
Cython : 0.29.30
pytest : 8.2.1
hypothesis : 6.108.2
sphinx : 5.0.2
blosc : 1.10.6
feather : None
xlsxwriter : None
lxml.etree : 4.9.1
html5lib : 1.1
pymysql : 1.0.2
psycopg2 : 2.9.3
jinja2 : 3.1.2
IPython : 8.10.0
pandas_datareader: None
bs4 : 4.11.1
bottleneck : 1.3.5
brotli : 1.0.9
fastparquet : 0.8.1
fsspec : 2023.10.0
gcsfs : None
matplotlib : 3.5.2+hrt1
numba : 0.59.0
numexpr : 2.8.3
odfpy : None
openpyxl : 3.0.10
pandas_gbq : None
pyarrow : 12.2.2.dev14+g99c7fc95e
pyreadstat : None
pyxlsb : 1.0.9
s3fs : None
scipy : 1.9.1
snappy : None
sqlalchemy : 1.4.49
tables : 3.7.0
tabulate : 0.8.10
xarray : 2022.6.0
xlrd : 2.0.1
xlwt : None
zstandard : 0.20.0
tzdata : 2022.1

[rhshadrach]

Thanks for the report! Agreed we should be modifying the index of an empty DataFrame here. It appears that modifying this line:

pandas/pandas/core/frame.py

Line 5708 in d11ed2f

if self.empty:

to be if self.empty and freq is None: will resolve this. Further investigations and PRs to fix are welcome!

[lfffkh]

Thanks for the report! Agreed we should be modifying the index of an empty DataFrame here. It appears that modifying this line:

pandas/pandas/core/frame.py

Line 5708 in d11ed2f

if self.empty:

to be if self.empty and freq is None: will resolve this. Further investigations and PRs to fix are welcome!

Hi, I've tried this before. I am new to the community, thanks for some tips you gave, I would like to continue to delve into this issue, can I take this？